Sensitisation of photographic silver halide layers for the silver dye beach process

ABSTRACT

THE SPECTRAL SENSITIVITY OF SILVER HALIDE EMULSIONS OF THE SILVER DYE BLEACH PROCESS IS INCREASED BY ADDITION OF UREA SUBSTITUTED MEROCYANINES OF THE FORMULA DEFINED BELOW.

United States Patent US. Cl. 96-140 '8 Claims ABSTRACT OF THE DISCLOSURE The spectral sensitivity of silver halide emulsions for the silver dye bleach process is increased by addition of urea substituted merocyanines of the formula defined below.

This invention relates to spectrally sensitized silver halide emulsions for color photographic materials for the silver dye bleach process, which contains merocyanine sensitizers.

It is known to produce color photographic images by the silver dye bleach process. This process is performed with uniformly colored photographic layers in which a silver image is produced by exposure and subsequent development. This silverimage may be a negative or positive of the original, depending on the nature of the process employed. After further treatment stages, such as fixing followed by heating, the dye is bleached imagewise in proportion to the amount of silver present, in a bleaching bath which is usually strongly acid. A color image which is a positive of the original is then obtained if the silver image was a negative of the original whereas a color image which is opposite in gradation to the original is obtained if the silver image used in the bleaching process is a positive of the original. .The image dyes used are generally azo dyes, and these include both water soluble dyes and insoluble pigments.

One of the serious disadvantages of the silver dye bleach process is that the sensitivity of the photographic layers is very substantially reduced by the fact that they are already colored before exposure. This is shown most markedly if the material is subjected to a complementary sensitisation of the kind which is usual for color photographic layers, in which the blue-sensitive layer is colored yellow, the green-sensitive layer is colored magenta and the red-sensitive layer cyan. In such a case, the sensitisation maximum coincides with the absorption maximum. of the image dye and the sensitivity of these layers is very considerably reduced. One of the great difficulties of this process therefore lies in the production of sufliciently sensitive layers and multi-layered products for the production of color photographic images by the silver dye bleach process. 7

Since the sensitivity of photographic emulsions can be very considerably increased by means of spectral sensitizers, these compounds are particularly important in this connection. Sensitizers for silver dye bleach materials must satisfy numerousrequirements above those which must be met for other conventional materials. In addition to good sensitisation properties, in particular as regards the form and height of the sensitisation maximum, the sensitizers must not deleteriously affect the stability of the silver halide emulsions, in particular the storage stability and stability under tropical conditions. In addition, the support, for example paper, or the layer-formng substance, e.g. gelatine, should not appear to be colored by the sensitizer after the photographic processing. Furthermore, the sensitizing dyes must be adsorbed 3,778,279 Patented Dec. 11,

'so firmly at the silver halide grain that they will not be displaced by the azo dyes. Itis known from conventional color-forming development processes that the basic cyanines are readily removed from the silver halide grain by color couplers which contain sulfonic acid groups and that they therefore cause only a very slight increase in sensitivity. In certain cases, they may even be shown to exert a desensitizing effect in the silver dye bleach process.

It is also known from German patent specification No. 1,083,124 to use betaine-cyanines as sensitizers for photographic layers for the silver dye bleach process. However, these sensitizers do not satisfy all the necessary requirements, since frequently they are not completely removed by the processing, thus causing a considerable coloring of the binder of the silver halide emulsion layer. This results in a coloring of the white image portions, especially in cases where the image dyes have low densities.

Merocyanines have also been described for use in the silver dye bleach process. These are neutral molecules which have no affinity for the binder. Merocyanines are completely different in their constitution from the abovementioned betaine cyanines. The: betaine cyanines have an electron deficiency distributed over the whole methine chain and thus carry a positive charge. This charge is compensated by acid groups with a negative charge which are attached to the molecule. The molecule accordingly has a betaine structure which can be caused to undergo structural changes by the addition of other organic or inorganic substances. Merocyanines, by contrast, do not carry a charge which is externally apparent.

Furthermore, merocyanines are largely inert not only towards the azo dyes of the photographic layers for the silver dye bleach process but also towards other additives, especially stabilisers, mordants such as biguanides or guanides used in the normal quantities, Wetting agents,

additives for influencing the viscosity properties of azo dyes in gelatine and/or photographic emulsions, various types of hardeners such as chrome alum or formaldehyde, and plasticisers such as glycerol.

On the other hand the sensitization effect of merocyanine sensitizers is often insuflicient.

It is among the objects of the present invention to provide for silver halide emulsion layers spectral contain an azo dye, which sensitizers which have a sufiiciently high i (I) R=(1) a saturated or olefinically unsaturated aliphatic group preferably containing up to 5 carbon atoms, e.g. methyl, ethyl, propyl, butyl or allyl, (2) aryl, particularly a group of the phenyl or naphthyl series, e.g. aor fl-naphthyl, or (3) cycloalkyl, e.g. cyclohexyl; the above-mentioned groups may carry further substituents, e.g. alkyl or an alkoxy group containing preferably up to 5 carbon atoms, thioalkyl which also preferably contains up to 5 carbon atoms, halogen such as chlorine or bromine, nitrile or hydroxyl; X=oxygen or sulfur;

Y=sulfur or selenium;

Z=a biltunctional, straight-chain or branched chain, saturated or unsaturated, aliphatic group containing preferably 2-6 carbon atoms and more particularly 3 or 4 carbon atoms, the aliphatic group may contain further substituents, e.g. hydroxyl, alkoxy or halogen such as chlorine or bromine;

R'=sulfo, sulfato, carboxyl or sulfonamide, in particular acyl-substituted sulfonamide, preferably sulfonamide groups which are substituted with an acyl radical which is derived from an aliphatic carboxylic acid which contains up to 5 carbon atoms; the above mentioned acid radicals may also be present in the neutralized form, e.g. as alkali metal salts, ammonium salts, etc.;

R"=(1) hydrogen, (2) alkyl preferably containing up to 5 carbon atoms which may be substituted, e.g. with phenyl or (3) aryl and in particular phenyl; R" preferably is a hydrogen atom;

R'=(1) hydrogen, (2) a saturated or olefinically unsaturated aliphatic group preferably containing up to 40 5 carbon atoms such as methyl, ethyl or allyl, these alkyl radicals being substituted if desired, e.g. with phenyl or (3) aryl, preferably phenyl, or (4) cycloalkyl; the above-mentioned radicals may contain further substituents, e.g. alkyl or alkoxy preferably containing up to 5 carbon atoms, halogen such as chlorine or bromine, carboxyl.

The following sensitizers have proved to be particularly 39 suitable:

0 CHr-NH-L-NH OaNa H -OH=CH, (A 12):

SOaH-N(C H)a (16) S 0 H om=0H-CH,Nn-ii-NH N =CH--CH :S

N g rim-whom 43H,

H-SOINE (17) f Se o i 02Hs-NH-JJ-NH N ('JH;-CH=CH; H, bH-Cl CH -S0:Na (18) propene sultone, chloropropane sultone or 1-ch1oro-2- s o t hydroxy-El-propane sulfonic acid:

CzHr-NH-ii-NH N H R--N=C=x HQN /CH; -b in, N

Y 311011 40 v x s HFSOINB 0 (19) m E =CH-CH =s N ll N The preparation of sensitizer 5 is described in detail below. Others are prepared in an analogous manner. SENSITIZER 5 omggocm 32 g. of Z-methyl-G-aminobenzothiazole and 350 cc. of (20) benzene are heated to about 60 C., 25 g. of cyclohexyl Y O X I R-NH-ii-NH CH: CzHgO-CH- Acetonltrll :Ha)|

The compounds of Formula II are obtained by the addition of isocyanates or isothiocyanates to the molecules of amino-substituted azoles in accordance with the equation given below, followed by quaternisation with a suitable quaternising agent, e.g. with propane sultone,

isocyanate are slowly added dropwise and the reaction mixture is then stirred for 4 hours. The reaction mixture is left to stand overnight and is then filtered through a suction filter. After recrystallisation of the precipitate from alcohol, the compound having the formula shown below is obtained. M.P.: 215 C.

Quaternisation is carried out by boiling 14 g. of the above mentioned base with 7 g. of propane sultone in cc. of anisole for 40 minutes. The quaternized product is then precipitated by the addition of acetone, 16.5 -g. of a quaternary salt of the following formula being obtained:

16.5 g. of the above salt are dissolved in 25 ml. of cresol at 120 C., a hot suspension of 9.6 'giof ethoxymethylene- N-allyl thiobarbituric acid in ethanol "and acetonitrileis added as well as 15 cc. of triethylamine and the reaction mixture is then briefly heated on a steam bath. A clear, deep-red solution is obtained at first but the dye begins to separate after only a few minutes. The reaction mixture is then suction-filtered while still warm and therecovered precipitate washed with methanol, ethanol and ether. Sensitizer is obtained by recrystallisation from methanol. M.P.: 243 C. absolute maximum absorption 507 nm.; 1 g. e=4.97.

The merocyanines for use according to the invention are particularly advantageous for sensitizing to green (500-600 nm.) highly sensitive iodide-containing silver bromide emulsions which contain magenta azo dyes. They are preferably added to the emulsion either individually or as mixtures in quantities of 20-600 mg. per mol of silver halide, preferably 70-450 mg. per mol of silver halide.

The sensitizing dyes of the present invention are distinguished from the known merocyanines, e.g. those mentioned in US. Pat. No. 3,401,404 by the fact that when used in the presence of azo dyes they result in strikingly steep sensitization curves, in particular a steep decay towards the long-wave region of the green part of the visible spectrum. This property results not only in a still greater improvement in the color separation and true color reproduction (with respect to the original) but also in increased darkroom safety so that processing is considerably facilitated.

The silver halide emulsion layers according to the invention which contain azo dyes have excellent stability on storage even under tropical conditions, and to digestion.

The present merocyanines are are superior to known merocyanines for example those described in US. patent specification No. 3,520,693 in that their sensitizing effect is substantially greater and in that they can be washed out more readily, discoloring of the washed layers being completely avoided.

The azo dyes used for the silver halide layers accord ing to the invention may suitably be those azo dyes already known for the silver dye bleach process, especially those which contain phenolic hydroxyl and/or sulfonic acid groups.

EXAMPLE 40 parts of a 1% aqueous solution of 6-methyl-4- hydroxy-1,3,3a,7-tetraazaindene, 40 parts of a 0.1% methanolic solution of sensitizer 2, 200 parts of a 2% aqueous solution of the magenta dye having the following formula.

Hogs-Goa 0.11

20 parts of a 5% aqueous solution of saponin and 20 parts of a 5% methanolic solution of 'N,N,N-tris-(acryloyl) hexahydrotriazine-( 1,3,5) are added successively with stirring at 40 C. to 1000 parts of a highly sensitive silver 10 (1) Development: 8 minutes in a bath of N,N-n butyl-n-w-sulphobutylphenylenediamine a *6 Hydroxylamine sulfate 4 Sodium sulfite 25 Potassium bromide 1 Sodium carbonate Dissolved and made up to 1000 ml. with water.

(2) Washing; 5 minutes.

(3) Hardening; 5 minutes in a bath of Formalin (30% aqueous solution) ml 70 Sodium bicarbonate ..g 5 Water up to 1000 ml.

(4) Washing: 5 minutes.

(5) Dye bleaching: 15 minutes in a bath of Quinoline ml 50 Sodium hypophosphite g 5 Potassium iodide g 10 Cone. sulfuric acid ml- 75 Water up to 1000 ml.

(6) Washing: 5 minutes.

(7) Bleach fixing: 15 minutes in a bath of G. Sodium carbonate anhydrous 24 Sodium thiosulfate anhydrous Tetrasodium ethylene diaminotetraacetate 26 Iron (III) chloride 15 Sodium sulfite anhydrous 13 Water up to 1000 m1.

S O k 1 E CH-CH =S N CHs-C O-NH The sensitometric measurements of the magenta dye wedges obtained show a maximum dye density of 1.3.

The increase in sensitivity over that obtained in the comparison sample is shown in the following table.

Increase in sensitivity in 3x/2-steps compared with Sensitising dye: the comparison sensitiser The same increase in sensitivity is obtained when the green sensitive silver halide gelatine emulsion layer described above is arranged in a multi-layered material as described, for example, in Example 4 of Belgian Pat. 730,611.

What is claimed is:

1. A light-sensitive photographic silver halide e rnulby at least one merocyanin'eof sion spectrally sensitized the formula:

tar-Z wherein 'R=(1) a saturated or olefinically unsaturated aliphatic group having up to 5 carbon atoms, (2) an aryl group of the phenyl or naphthyl the substituted groups may be substituted by alkoxy or alkyl-thio groups containing up to 5 carbon atoms,

chlorine, bromine, nitrile stituent aryl group may be substituted with an alkyl group containing up to 5 carbon atoms;

X=oxygen or sulfur; Y=sulfur or selenium;

Z=a bifunctional straight or branched saturated or unsaturated aliphatic chain; R'=sulfo, sulfato, carboxyl R"-=hydrogen, alkyl or aryl; and

R"'=(1) hydrogen, (2) a saturated or olefinically unsaturated aliphatic group having up to 5 carbon atoms, or (3) an aryl group or a cycloalkyl; the substituent groups may be substituted by alkoxy or alkylthio groups containing up to bromine, carboxyl and the substitutent aryl group may be substituted with an alkyl group containing up to 5 carbon atoms.

wherein R" stands for hydrogen. a V

wherein R represents 'a saturated or olefinically 'unsaturated aliphaticgroups having up to 5 carbon atoms;

N v wherein R represents allyl.

=S 5. The'light-sensitive photographic material of claim 1,

| wherein the merocyanine has the following formula: I 0 y r SOaNa series, or (3) a cycloalkyl;

or hydroxyl and the sub- 0 6. The light-sensitive photographic material of claim 1, wherein the merocyanine has the following formula:

or sulfonamide;

CH: C H=CH1 SOaNa 5 carbon atoms, chlorine,

7. The light-sensitive photographic material of claim 1, wherein the merocyanine has the following formula: 1

8. The light-sensitive photographic material of claim 1,

s 0 cH,=oH-oHiNH-iLNH =CH-CH= =s N \N V orr-on (HZ)! P 7' "'1 SOaH- 2H5)I References Cited UNITED STATES PATENTS 3,438,774 4/1969 Depoorter et a1. 96-140 3,520,693 7/1970 Gotze et al. 96-142 NORMAN G. TORCHIN, Primary Examiner R. L. SCHILLING, Assistant Examiner US. 01. X.R. 96-142 2. The light-sensitive photographic material of, claim 3. The light-sensitive photographic material of claim f l',

4, The light-sensitive photographic material of claim 1,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,77 79 Dated 1 973 Inventor(s) Johannes Gotze at 8.1

It is certified that error appears in the above-identified patent I and that said Letters Patent are hereby corrected as shown below:

Front page column 1, line 5, the inventor's name should.

read: Johannes Gotze Column 4, in the first formula "SO NO" should be replaced 7 Column 7, lines 60-65, a double-bond should be inserted in the heterocyclic ring of formula II. I

Signed and sealed this 30th day r April 197E.

(SEAL) Attest:

EDWARDI/LFLETCHEILJR. I I c MARSHALL DANN Attesting Officer Commissioner of Patents 

